Determination of geometric orientation of adsorbed cinchonidine on Pt and Fe and quiphos on Pt nanoclusters via DRIFTS

Platinum nanoclusters modified with cinchonidine have been employed as 'quasi-homogeneous' catalysts for the hydrogenation of ethyl pyruvate and have demonstrated exceptional activities while the ee's of these systems are currently inferior to the traditional Pt/Al2O3 heterogeneous system. For the bulk systems it has been shown that the orientation of the modifier on the metal surface is a critical parameter influencing catalytically induced enantioselectivity. It has been speculated that the lower observed ee's for the nanocluster systems are a result of the modifier assuming an orientation unfavorable for inducing enantioselectivity due to the lack of large numbers of planar metal atoms. Using DRIFTS (diffuse reflectance infra-red Fourier transform spectroscopy) analysis of samples together with geometry optimization and IR modelling we have studied the orientation of cinchonidine on Pt and Fe nanoclusters and additionally the man-made ligand quiphos on Pt nanoclusters. It has been determined that cinchonidine can adsorb on Pt and Fe nanoclusters in both 'flat' and 'tilted' modes, while quiphos can be adsorbed on Pt only via the 'pi-bonded' mode. These studies thus provide an insight into modifier orientation on nanocluster surfaces that can be extended to a wide range of potential modifiers and facilitate a better understanding of the origin of enantioselectivity with these 'quasi-homogeneous' catalyst systems.     

A high power hybrid mid-IR laser source

An efficient hybrid mid-IR laser system comprising a thulium fibre laser, Ho:YAG solid state laser and a zinc germanium phosphide optical parametric oscillator is presented. A 790 nm diode pumped 1908 nm thulium fibre laser operating at 30 W pumps an RTP q-switched Ho:YAG laser emitting 17 W at 40 kHz and 2090 nm. The zinc germanium phosphide optical parametric oscillator efficiently converts this into the 3-5 μm region producing 10.1 W with 59% optical conversion efficiency and an M² = 1.5.     

The Stein phenomenon for monotone incomplete multivariate normal data

We establish the Stein phenomenon in the context of two-step, monotone incomplete data drawn from , a (p+q)-dimensional multivariate normal population with mean and covariance matrix . On the basis of data consisting of n observations on all p+q characteristics and an additional N−n observations on the last q characteristics, where all observations are mutually independent, denote by the maximum likelihood estimator of . We establish criteria which imply that shrinkage estimators of James-Stein type have lower risk than under Euclidean quadratic loss. Further, we show that the corresponding positive-part estimators have lower risk than their unrestricted counterparts, thereby rendering the latter estimators inadmissible. We derive results for the case in which is block-diagonal, the loss function is quadratic and non-spherical, and the shrinkage estimator is constructed by means of a nondecreasing, differentiable function of a quadratic form in . For the problem of shrinking to a vector whose components have a common value constructed from the data, we derive improved shrinkage estimators and again determine conditions under which the positive-part analogs have lower risk than their unrestricted counterparts.     

Probing folded and unfolded states of outer membrane protein a with steady-state and time-resolved tryptophan fluorescence

Steady-state and time-resolved fluorescence measurements on each of five native tryptophan residues in full-length and truncated variants of E. coli outer-membrane protein A (OmpA) have been made in folded and denatured states. Tryptophan singlet excited-state lifetimes are multiexponential and vary among the residues. In addition, substantial increases in excited-state lifetimes accompany OmpA folding, with longer lifetimes in micelles than in phospholipid bilayers. This finding suggests that the Trp environments of OmpA folded in micelles and phospholipid bilayers are different. Measurements of Trp fluorescence decay kinetics with full-length OmpA folded in brominated lipid vesicles reveal that W102 is the most distant fluorophore from the hydrocarbon core, while W7 is the closest. Steady-state and time-resolved polarized fluorescence measurements indicate reduced Trp mobility when OmpA is folded in a micelle, and even lower mobility when the protein is folded in a bilayer. The fluorescence properties of truncated OmpA, in which the soluble periplasmic domain is removed, only modestly differ from those of the full-length form, suggesting similar folded structures for the two forms under these conditions.     

Spin-orbit coupling constants from semi-empirical wavefunctions

The problem of computing spin-orbit coupling constants from wave-functions of a semi-empirical variety are considered specifically for SCF wavefunctions with intermediate neglect of differential overlap. The incorporation of the 1s electrons into a ‘core’ should result in an effective nuclear charge of Z′ = Z - 2·5846 being used in one-electron terms, but for agreement with experiment the results have to be reduced by some 70 per cent. This reduction factor is different for ions. If the multiplicative factor is included good agreement between observed and calculated spin-orbit coupling constants is given.     

Deflection of sputtered ions by surface charges

The trajectories of ions sputtered from an insulating surface carrying a surface charge have been computed. The results show that yields measured in particular directions can be in serious error as the trajectories of low energy sputtered ions depend critically on surface charge and point of origin of the ion. The distorted yield curves for 1.2 eV ions and 10 eV ions leaving a surface with a ten volt surface potential are calculated.     

Modelling toolkit to assist with introducing a stepped care system design in mental health care

We describe a modelling toolkit that was developed with the aim of assisting those responsible for introducing stepped care systems to local mental health services in the UK. The toolkit was pre-populated with real patient flow data collected from four sites that piloted the stepped care system design. Two analytical models were developed and coded as part of the toolkit to provide insights concerning workload, patient throughput, and changes in waiting times and waiting list size. An interface was built to allow users to specify their own stepped care system and input their own estimates or data of service demands and capacities at different steps. Despite the challenges and limitations, the use of modelling to inform the design of new service configurations is an important step in the right direction and we would recommend this as a reasonable way forward.     

An EPR characterisation of stable and transient reactive oxygen species formed under radiative and non-radiative conditions

Research on Chemical Intermediates - Electron paramagnetic resonance (EPR) spectroscopy is the ideal method of choice when detecting and studying the wide variety of paramagnetic oxygen-centred...